A riser is made up of an assembly of tubular elements of length ranging between 15 and 27 m (50 and 90 feet), assembled by connectors. The tubular elements generally consist of a main tube provided with connectors at each end. Tubular auxiliary lines, also called peripheral lines, commonly referred to as “kill line”, “choke line”, “booster line” and “hydraulic line”, allowing circulation of technical fluids, are provided parallel to the main tube. The tubular elements are assembled on the drilling site, from a floater. The riser is lowered into the water depth as the tubular elements are assembled, until it reaches the wellhead located on the sea bottom.
In the perspective of drilling at water depths that can reach 3500 m or more, the weight of the riser becomes very penalizing. This phenomenon is increased by the fact that, for the same maximum working pressure, the length of the riser requires a larger inside diameter for the auxiliary lines, considering the necessity to limit pressure drops.
Besides, the necessity to decrease the riser assembly time is all the more critical since the water depth, and therefore the riser length, is great.
Documents FR-2,925,105, FR-2,956,693 and FR-2,956,694 describe various solutions notably aiming to involve the auxiliary lines, together with the main tube, in the taking up of the longitudinal stresses applied to the riser. However, for the systems described in these patents, fastening of the auxiliary lines with respect to the main tube leads to high tensile stresses in the auxiliary lines. In order to withstand these tensile stresses, the auxiliary lines have great thickness values, which generates an increase in the mass and size of the floats, and therefore in the cost of the riser. Furthermore, the connectors provided in these patents are not entirely dismountable, which makes inspection and maintenance of the riser difficult.
The present invention describes a solution providing a compact connector design with a locking ring arranged between the main tube and the auxiliary lines. The connector according to the invention is well suited for deep-sea risers, i.e. located at depths greater than 2000 meters. Furthermore, the connector according to the invention is dismountable, and problems of auxiliary line connection interference are limited.